Structure of Real Functional Elements

A further feature of the structure of the functional domain arises from the central role of the irreducible element in the description of functionality and the definition of that element, as depicted in Fig. C4.4. Due to this view of an engineering project as an optimisation of the balance between cost and revenue, the secondary elements fall into two completely separate categories the elements describing aspects of the cost, and the elements describing aspects of the performance, as already mentioned at the end of Sec. C4.3 and illustrated in Fig. C4.6. 

Following on from the structure of the functional domain, real functional elements, as a system of imaginary elements, wiU also have certain structural features. To see how this comes abouL consider a particular project and develop, at firsL the plant s capability, i.e. what it must do, as a system of primary functional elements. The elements and structure of that system will, of course, depend both on the required capability and on our choice of functions to achieve it. However, once that system has been created, and we turn to describing the cost of providing the functions and the additional requirements on such aspects of the performance as reliability, maintainability, and safety, the corresponding elements refer to the primary elements. That is, the primary elements form what we might think of as a skeleton structure, and the secondary elements dress up this skeleton to form a real elemenL thereby inheriting some of the same structure. 

When we say some of , it is because the extent to which the secondary elements inherit the structure of the primary elements depends on the type of element. The cost elements will inherit the subdivision into functions, but will not 

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